EP3129725A1

EP3129725A1 - Lightweight, low-cost heliostat mirror for concentrating solar power

Info

Publication number: EP3129725A1
Application number: EP15776061.2A
Authority: EP
Inventors: Gyula Greschik; Arthur L. PALISOC
Original assignee: LGarde Inc
Current assignee: LGarde Inc
Priority date: 2014-04-07
Filing date: 2015-03-09
Publication date: 2017-02-15
Also published as: US10036878B2; EP3129725A4; US20190041618A1; US10642011B2; US20150286039A1; WO2015156941A1

Abstract

Systems and methods are described herein that may be used to form a heliostat. Various reflective surfaces and support structures are described that permit lightweight construction of configurable heliostats.

Description

Lightweight, Low-Cost Heliostat Mirror for Concentrating Solar

Power

PRIORITY

(0001 j This application claims priority to U .S . Application No. 61/976,42 , filed

April 7,, 2014, titled "Lightweight, Low-Cost Heliostat Mirror for Concentrating So!ar Power;" and U.S. Application No, 62/088,167, filed December 5, 2014, titled "Lightweight, Low-Cost Heliostat Mirror for Concentrating Solar Power," each of which are incorporated by reference in its entirety into this application,

BACKGROUND

(0002 J One approach to solar electric power generation is to use one or more heliosiats to heat and focus reflected solar radiation onto a container of high-specific-heat material. A heliostat is basically a flat plate with a highly reflective surface to efficiently reflect most of the solar radiation incident upon it onto the target container (the "receiver"). To accompl is this, the heliostat must be capable of tracking the sun across the sky and pointing the reflective surface in the appropriate direction to maintain the son's reflected radiation on the container, in its most basic form, the heliostat is a simple planar support structure, coated with a highly-reflective optical material and mounted on a tracking/pointing pedestal. The desirable qualities of a state-of-the-art heliostat are lightweight, low-cost, structurally rigid, environmentally durable, with a highly reflective surface. In improved designs, a very slight curvature i the heliostat. mirror is introduced to enhance the focusing quality,

SUMMARY

|0003] A new type of heliostat .mirror and support structure are provided herein that make use of a novel design and material combinations.

(0004] An exemplary heliostat according to embodiments described herein may include a light weight support with one or both opposing surfaces coupled to a reflective material. The support, one or both opposing surfaces, and/or the reflective material may be flat or contoured. The light weight support .may be, for example, a foam base. The reflective surface may be, for example, a metal sheet, mirrored film, or combinations thereof.

(0005] An exemplary heliostat according to embodiments described herein may include a support structure in which two or more sections are designed to be identical or mirror image duplicates. The exemplary heliostat may include attachable centerpieces between two or more of the identical or mirror image duplicate sections to control a desired shape of the heliostat. Therefore, the support structure may permit, a configurable

arrangement including a selec table curvature of the segments by interposing different centerpieces.

|0 O6{ An exemplary heliostat according to embodimen ts described herein may include a support structure in which a first and second support, structures are used to support a plurality of panels. The first support structure may include one or more components such as the wing and centerpiece configuration. The first support structure, second support structure, and combinations thereof may comprise interchangeable components such that the design of the heliostat may be configured by using selectable components. For example, curved or straight second support structures may be interchangeable, to impose a desired curvature to the heliostat panels.

DRAWINGS

{0007] Figure 1 illustrates a cross section of an exemplary heliostat panel as described herein.

(0008] Figure 2 illustrates an exemplary heliostat according to embodiments described herein. jO0O9| Figures 3 A and 3B il lustrates an exemplary support structure comprising three partitioned sections. Figure 3A is a top perspective view, while Figure 3B is a side cross- sectional view.

{0010} Figures 4 A and 5 A illustrate exemplary top elevation views of a heliostat according to embodiments described herein, while Figures 4B and 5B illustrate side elevation views of the exemplary embodiments of Figures 4A and 5A, respectively. (08111 Figure 6 illustrates an exemplary centerpiece including a precision surface and support structure.

(001 ] Figure 7 illustrates an exemplar support structure embodiment for use with a plurality of precision surfaces to form a heiiostat.

(0013] Figure 8 illustrates an exemplary curvature imposed on an exemplary support structure.

[0014] Figure 9 illustrates an exemplary cross section of an exemplary support structure section to retain a panel in place.

[0015] Figures 10A and 10B illustrate exemplary cut away features of an exemplary support structure for coupling portions of the support structure together.

(0016] Figure 1 1 illustrates an exemplary prismatic wing construction including removable battens and diagonals for collapsible storage.

DESCRIPTION

(0017] The following detailed description illustrates by way of example, not by way of limitation, the principles of the invention. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. It should be understood that the drawings are diagrammatic and schematic representations of exemplary embodimems of the invention, and are not limiting of the present invention nor are they necessarily drawn to scale.

[0018] Although embodiments of the invention may be described and illustrated herein in terms of a heiiostat comprising panels and support structures, it should be understood that embodiments of this invention are not so limited. Any combination of features described herein ma be used singularly or in an combination to create an structure. Components or features from different embodiments therefore, can be duplicated, removed, integrated, separated, or combined with any other feature to achieve any combination of benefi ts described herein. jO019} FIG. 1 illustrates a exemplary cross-section of a heiiostat mirror according to embodiments described herein. In an exemplary embodiment the design for a solar concentrating beliostat may include a lightweight base 4 with one or both opposing surfaces coupled to metal sheets 6. As shown, a rigid foam is used as the lightweight base 4 with both opposing surfaces coupled to metal sheets 6. The metal sheets 6 may be coupled to base layer by any method, including, for example, chemical and/or mechanical methods of an adhesive 8, bonding, bolting, mating surfaces, screwing, etc. The base 4, opposing surfaces, metal surfaces 6, or any combination thereof may be flat or contoured. The metal sheet 6 may be highly polished to provide the reflective surface or coupled to a mirror film 12. The mirror film may include one or more layers of material , such as a base or backing layer and an outer metallic or reflective layer. A moisture barrier 14 may also be applied and enclose the heiiostat or may be applied just along the edges or lateral sides of the opposing surfaces to seal the terminal ends and space between the respec tive layers. Any combination of the described features and embodiments may be used, such that components may be added, duplicated, subtracted, and recombined.

{0020] The exemplary lightweight base 4 may be used to provide the support structure for the heiiostat and/or the shape of the heiiostat. In an exemplary embodiment, the lightweight base 4 comprises a rigid foam. Exemplary rigid foams ma include rigid expanded polystyrene (EPS), rigid polyurethane foam, epoxy foam, and carbon-reinforced foam.

(0021 ] Adhesives 8 may be used to bond the metal sheets to the foam support structure, in an exemplary embodiment, the adhesive is impervious to the weather and performs o ver a large temperature range. Examples of exemplary adhesives may include epoxy. silicone, urethane, polystyrene and polyester based adhesives in both liquid heat activated, hot melt, and spray on formats,

10022} Thin metal sheets 6 may fully or partially cover one or more surfaces of the lightweight base 4, The thin metal sheets 6 can he, for example, stainless steel, aluminum, or titanium. The thin metal sheet may include a highly reflective or polished surface or may include a film to create the mirror surface. The thin reflective film may be eliminated if the top metal sheet used is a mirror-finish surface like mirror or super-mirror finish aluminum, minor or super-mirror finish stainless steel, and mirror or super-mirror finish titanium. [0023] If a thin reflective mirror film 12 is used, it may be made of one or more layers. An exemplary reflective mirror fi lm 12 may be made of a thin polymeric material coated on the outer surface with a thin layer of reflective material, such as a metal. The reflecti ve mirror .film hacking is typically comprised of materials such as thin polyinikle, polyester (PET), polypropylene (OPP), polyethylene (PE), polyvinyl (PVC), nylon (BON), and polycarbonate (PC) film, In order to make the thin fi!m reflecti ve, a thin layer of silver or aluminum coating may be deposited on one surface. Exemplary embodiments described herein incorporate a minor film. Film is understood to include any thin structure including, but not limited to, membrane, sheet, covering, coating, and combinations thereof.

[00241 For added protection against the e vironme t, a moisture barrier 14, such as a moisture barrier rubber paint, ma be applied ail around the edges. For example, a moisture barrier 14 my enclose or cover the terminal ends of the respecti ve layers of the lightweight base 4, metal sheets 6, and reflective mirror 12 to prevent separation of the layers. The moisture barrier 14 may also fully enclose the heliostat structure and contact the exterior surfaces of the reflective mirror film 12, the opposing thin metal sheet 6 or back side of the base 4 if a second metal sheet is not included, as well as the terminal ends of the respective layers, or any combination thereof Other materials that can comprise an effective moisture barrier may include poSyurethanes. acrylics, ethylene acrylic, nitrile, styrene butadiene, silicones, neoprenes, and epoxy.

[0025] An exemplary configuration is illustrated m Figure i . The solar concentrating heliostat 2 includes a lightweight rigid foam 4 backing wi h thin metal sheets 6 coupled, such as by bonding, on both surfaces. On one of the metal surfaces 6 is coupled, such as by bonding, to a very highly reflective and lightweight mirror film 12. The mirror film is made of a thin polymeric material coated on the outer surface with a thin layer of silver or aluminum on top of which is deposited a protective layer against oxygen and ultraviolet light. An exemplary embodiment uses EPDM™ .rubber paint, stainless steel metal sheets, a rigid foam of expanded polystyrene (EPS), the adhesive polystyrene foam insulation adhesive and a mirror film constructed from silver-coated polyimide thin film.

[0026] Embodiments described herein incorporate very low-cost, lightweight materials while simultaneously maintaining an extremely accurate surface quality. Our analytical models indicated that rms slope errors on the order of 0.15 milli-radians were achievable with this design. Consequently, two 1 -meter by 1 -meter in area by 4 inch thick prototype concentrators have been built and measured for surface quality. Figure 2 illustrates an exemplary one meter by one meter heiiostat sub-facet prototype built according to embodiments described herein. This prototype heiiostat sub-mirror facet was measured using precise photograimnetry to have an mis slope error of 0, 15 milli-radians.

|Θ 27| Embodiments of the present, disclosure also include proprietary methods for manufacturing and assembling the heiiostat. Exemplary features of our production method include the use of mch-by-mch attachment, such as by bonding, of the mirror film to the stainless steel sheet using Teflon-coated rollers to apply pressure on the mirror film for stronger initial adhesion, and vacuum-ba¾aina to assure excellent adhesion and prevention and elimination of bubbling. The fabrication may be automated using a roll-to-roll method wherein the thin metal sheets 6 are dispensed from a roller and applied onto either surface of the lightweight base 4 using a third roller. Adhesive application may also be automated by the use of jet nozzles. As the lightweight base 4 with the thin metal sheets 6 already bonded moves on a conveyor belt to the next section of the assembly line, the mirror film 12 may be applied to one of the metal sheets 6. This step is not necessar if one of the two metal sheets 6 used is already a reflective mirror.

(0(128) The novel heiiostat design described above may include several innovative support structures for the reflective panel that can reduce system cost and weight over conventionally-used structures.

10029] Figures 3 A and 3 B illustrates an exemplary support structure comprising three distinct parts joined to form a unit. Figure 3 A is a top perspective view, while Figure 3B is a side cross-sectional view in which the back support 36 and surface structure 38 are

exaggerated and separated for illustration only. A support structure with three distinct parts may include, for example, two wing sections 32 and a central section 34. As shown, two mirror symmetric identical wings and a centerpiece are provided on which the wings are mounted. The centerpiece, in turn, is mounted on an appropriate external structure (not shown), such as a pedestal or column. The wings and centerpiece may be coupled directly or indirectly. For example, and external frame ma be used to wedge or support parts together, or the parts may be bonded, adhered, jointed, hinged, mating surfaces, or otherwise attached.

10030] The wings and centerpiece can be constructed from different materials, such as, for example, galvanized steel or aluminum. |β8311 The wings may be straight or (slightly) carved. Curvature provides more accurate focusing of the sun's rays onto the target vessel. The curvature may be, for example, circular or parabolic .

(0032] El ements of the precision reflecti ve surface may be mounted over the wings alone or over the wings as well as over the centerpiece. Figures 4A and 4B illustrate an exemplary configuration m which the reflective surfaces are mounted over the wings alone. The centerpiece section of the support structure is therefore exposed along the top surface . Figures 5A and SB illustrate an exemplary configuration in which the reflective surfaces are mounted over the wings and center piece together. This configuration allows the formation of two separate surfaces (over the wings) of a single continuous surface of the entire structure. Figures 4A and 5 A illustrate exemplary top elevation views of exemplary embodiments of a heiiosta while Figures 4B and 5B illustrate side elevation views of exemplary embodiments of the heliostats of Figures 4A and 5 A, respectively.

(Θ033] in an exemplary embodiment, a. slight curvature of the supported surface in the wing-wing direction is approximated by the centerpiece's shape which, by its geometry, orients the wings in a slightl convergent manner. For example, as illustrated by the side elevation views of Figures 4B and 5B, the profile of the centerpiece support structure may be tapered such that a top length of the centerpiece is less than a bottom length of the centerpiece. Figure 6 illustrates an exemplary centerpiece including a precision surface 38 and support, structure 36. As shown, the bottom surface of the support structure has a wing- wing length of 1,1 , while a top surface of the support structure toward or adjacent the reflective surface has a length L2. As shown, LI is greater than L2. The exterior edges 62, 63 of the centerpiece abut the support structure of the wings and are configured to orient the wings at a desired angle relative to the centerpiece section. The support structures of the wings may be generally rectangular in wing-wing cross-section or may themselves be slightly tapered. The surface structure 38 may comprise the reflective surface/precision surface. The surface structure 38 may have a wing-wing length of L3. The surface structure length L3 may be equal to or less than the top surface length L2 of the support structure adjacent the surface structure. The length L3 may be less tha L2 for tapered profiles to prevent the surface structures from interfering in the angled configurations. j(HI34] By controlling wing-wing curvature by the centerpiece shape alone, the fabrication of a high number of structural units (each consisting of the precision surface and its support) with different wing-wing curvatures is made economical Specifically, the wing sections may be uniformly made and a wing-wing curvature can be achieved by simply exchanging different centerpieces of greater or less tapering profiles. The shape of the centerpiece is determined by the distance of the heliostat structure from the target vessel, with less curvature required as the distance between heliostat and target increases. A lesser wing- wing curvature can be achieved with less taper, or a more rectangular shaped support structure.

(0035] For example, a middle section of a iri-seetional configuration, is

interchangeable in the sense that there may be typically several such al entative mid-sections pre-fabricated, and on any of these the same wings can be mounted on the two sides. Due to the slight

differences of the geometries of the center elements, the pair of wings (and the center element) end up constituting a somewhat concave mirror, the concavity of which depends on the central element used. The need for mirror concavity is a function of location in the heliostat field; mirrors nearer the receiver have to be more concave than those farther away. Accordingly, center pieces of certain shapes will end up being used in certain continuous areas/regions within the heliostat field, making the mirrors there have identical shapes - but somewhat different shapes from mirrors in other areas of the heliostat field.

(0036] So, on the one hand, the primary support includes the wing, center, wing as illustrated, but, because the center in this triplet is not exactly identical across the heliostat. field, the illustrated wing, center, wing structure still does not require exact geometric uniformity

for all heliostat. units.

(0037] The construction concept of different center pieces used across the field aims at eliminating the need for geometric tuning by nuts, screws, and other devices, otherwise necessary if different heliostat. shapes are needed. By using a set of slightly different prefabricated center pieces instead, nothing needs to be adjusted on the construction site, instead, simply, the right type of centerpiece has to be used. This is faster and simpler if welt managed..

[0638] Figure 7 illustrates an exemplary support structure embodiment .for use with a plurality of precision surfaces to form a larger heliostat, In an exemplary embodiment, precision surfaces may include their own support structure such as the partitioned support structures described above with respect to Figures 4A and 4B, Figures 5A and SB, or a combination thereof, or may be individual structures as described with respect to Figure 1. Each surface supported by the proposed structure is constituted by a multitude of indi vidual panels which are mounted by an appropriate means on a larger support structure, in order to facilitate the mounting of the indi vidual panels on their support, the larger support comprises at least one primary support al igned in the wing-wing direction (consisting of the two wings and the centerpiece) and secondary support in the peipendicular direction from the wing- wing direction.

[0039] Figure 7 illustrates an exemplary support layout 70 and mounting of individual panels 76 according to exemplary embodiments. The support layout 70 may .include a primary support 72 in a wing- wing or first direction. A second support 74 may be included in a second direction generall perpendicular to the first direction. The second support system 74 .may include a plurality of rails such that individual panels 76 are retained between two adjacent rails 74. The rails may be configured or spaced such that the same or different panel configurations may be positioned anywhere in the rail structure. The primary support 72 may be coupled to a base 78 to orient the heliostat in a desired direction toward the sun. 0040] The support layout 70 may be configured to take advantage of the wing-wing curvature control through interchangeable, unique centerpieces and common, identical wings to permit low cost production of adjustable or dynamic designs. The primary support 72, for example may include two wings 80 of mirror symmetry and a centerpiece 82. The wings and center piece may be coupled together to form a unitary primary support 72. The center piece support, can be configured to angle the panels of the wings rela tive to the face or panels of the centerpiece. As shown, the downward projection of the centerpiece and wings is shown in dotted lines below the heliostat 70. The cross sectional shape of the illustrated centerpiece is square or rectangular, thus aligning the wings parallel or flat relative to the centerpiece. The centerpiece cross-section may be tapered as described above to impose an angle to the wings relative to the centerpiece.

[0041] The secondary support elements 74, 74" may include rails of prismatic cross section which may be straight 74 or may be (^"slightly) curved 74' as indicated in Fig. 8 to give the supported surface a secondary curvature in the rail direction (perpendicular to the curvature in the wing-wing direction, controlled by the centerpiece). Figure 8 illustrates a exemplary slight curvature in the indicated second direction thai is achieved with curved rails. The curvature shown in the figure is exaggerated for illustration purposes. The rails may be configured to accept planar or substantially planar panels while still imposing an angle between adjacent panels from the curvature of the rails 74'.

|u042j Figure 9 illustrates an exemplary cross section of a rai l 74, 74' configured to retain a panel 76 in place. The rail cross sections have flanges 92 such that the panels 76 which constitute the surface itself can be piaced (slid) between adj acent pairs of the parallel rails on each end between the rail flanges that prevent panel removal in all directions except sliding along the rails. As shown, a rail may include a first flange and second flange at opposing ends of the rail. When positioned in the support structure 70, the flanges extend from the rail in a direction of the primary support, indicated in figure 7. or parallel to the face of the heliostat or panels. The flanges may he positioned at a front and rear side of the rail The bottom and/or top of the rail may also include a stopper such that a panel may be slid along the rail until encountering the stopper. In an exem lary embodiment, the rail bottom terminal end comprises a stopper such that the first panel rests against the stopper. The next panel then rests on the first panel, and the panels are stacked on top of each other and held in place in the forward and rearw ard direction by the flanges of the rails. The motion of the panels, once slid betwee the flanges of adjacent rail pairs, may also be arrested at any convenient position by wedging them between the rail flanges. This is show in Figure 9. Therefore, the separation of in terior facing surfaces of opposing flanges on a rail may ha ve a first separation distance greater than the thickness of a panel positioned within the rail. A wedge 94 or secondary material may be positioned between the panel and one of the flanges such that the panel is held stationary relative to the rail 74 by frtctional engagement,

[0043 j The cross section shape described hi the previous paragraph may be achieved with standard l-beams, by combining other standard structural profiles such as a pair of C channels back-to-back, or by a unique design.

{0044] The rails may also be mounted on the primar support by a rapid lock mechanism. The rapid lock mechanism between rails and primary support may include protrusions on one component and slots on the other where the protrusions fit, and holes across that are aligned when the protrusions are inserted, fasteners (bolts, rivets, wedges, pegs, etc.) can be driven through these holes to firmly attach the secondary rails 74, 74' to the primary support 72. The type of fastener to use depends on specific needs, e.g., on the need to rapid release or the lack thereof, or the need for precision.

[0045] Figures 10A and JOB illustrate art exemplary connection configuration between the rails 74, 74' and the primary support 72. Figure !OA illustrates an exemplar).' rail sliding on tongue openings, while Figure I OB illustrates the tongue between channels clamped, through web openings. The primary support 72 therefore may include a generally planar surface wit a protrusion or tongue 102 extending from the face thereof. The protrusion may be generally planar and extend in a direction parallel to the direction of the rails, or perpendicular to the wing-wing direction, or perpendicular the direction of the primary support. The protrusion may include a hole 104 that corresponds to a similar hole 104' on the rail 74. The rail 74 may include two generally planar, parallel surfaces 106 coupled by a gusset plate 108. Each generally planar, parallel surface 106 may include a flange 92 at opposing ends extending generally perpendicular to the planar surface. The flange 92 may include a second projection or curvature such that an end of the flange extends further over the planar surface than a portion of the flange near the plana surface, in other words, a thickness of the flange near the planar surface is less than a thickness of the flange away f om the surface near the terminal end of the flange. The fl ange therefore defines a channel for a panel to slide into. The tongue 102 of the primary support 72 fits into a space defined by the gusset plate 108. When the holes 104, 104', align, the rail may be anchored to the primary support,

[0046} The wings 1 100 of the primary support 72 may be trusses of triangular cross sec tion. The lateral struts (battens 1 102 and diagonals 1 104} on one face of the trass wings may be removable to permit. nested stowage and shipping. Figure .1 1 illustrates an exemplary prismatic wing construction includin removable battens and diagonals. These removable struts may also be a combination of rigid struts and cable links, which can be easily and rapidly engaged at their final locations and robustly held there by pretensioning.

{0047] The precision surfaces described herein may he used with any support structures, such, as any combination of support structures described herein or conventional support structures, in an exemplary embodiment, the support structure 36 of Figures 3-6 ma be the support structure of the reflective surface, such as described with respect to Figure 1 , 4 or 6, or may be a secondary support structure in addition to the structures of Figure 1. In an exemplary embodiment, the exemplary support structures may be used in conjunction such that a first support structure for the reflective surface may be used in accordance with Figure i that is mounted or shaped in a partitioned configuration of Figure 3. which is then incorporated into a larger structure according to Figure 7. The support structures of Figures 3-7 may be used with any reflective or precision surface and not just those of Figures 1. ju048j Embodiments described herein may be used to dynamically configure a heliostat. The configuration of the heliostat ma be configured such as to impose a desired curvature in one or more directions. As used herein, "curvature" is not limited to a continuous curvature, such as parabolic or ell iptic smooth curves or surfaces, instead, as used herein "curvature" includes a step-wise or piecewise curvature defined by adjacent planar or linear segments angled with respect to each other to form a perceived curvature along an entire length. Therefore, a heliostat face ma be considered curved by the selected orientation and position of adjacent planar panels.

[0049] Although embodiments of this invention have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and

modifications are to be understood as being included within the scope of embodiments of thi invention as defined by the appended claims.

Claims

CLAIMS The invention claimed is:

1. A heiiostat, comprising; a plurality of panels compr ising a refleci i ve surface; and a support structure for orienting the plurality of panels in a desired configuration relative to each other,

2. The heiiostat of claim 1, wherein, the plurality of panels comprise: a lightweight base support having a first surface and a second surface opposite the first surface: a metal sheet covering at least a portion of the firs t surface; a reflective surface on the metal sheet.

3. The heiiostat of claim 2, wherein the lightweight base support comprises a rigid foam.

4. The heiiostat of claim 3 , wherein the reflective surface is a surface of the metal sheet.

5. The heiiostat of claim 3, wherein the reflective surface comprises a film on the metal sheet,

6. The heiiostat of claim 5_t wherein the .film comprises a thin polymeric material coated on an outer surface of the metal sheet with a thin layer of reflective material comprising metal.

7. The heiiostat of claim 3, further comprising a moisture barrier around at least a portion of the panel.

8. The heiiostat of claim 1₅ wherein the plurality of panels comprises at least three panels including two wing panels and a. centerpiece panel

9. The heiiostat of claim 8, wherein the wing panels are mirror opposites on opposing sides of the centerpiece panel

10. The heiiostat of claim 9, wherein the centerpiece panel is shaped to impose a desired orientation of the wing panels relative to the centerpiece panel.

11. The heiiostat of claim 10. wherein a width of the centerpiece panel is tapered such that when adjacent edges of the wing panels rest against edges of the centerpiece panel, a front face of the wing pane! is angled greater than 0 degrees relative to a front face of the centerpiece.

12. The heiiostat of claim 1, wherein the support structure comprises a primary support having a first direction and a plurality of secondary supports having a second direction, different from the first direction,

13. The heiiostat of claim 12, wherein the plurality of secondary supports comprises a plurality of rails, adjacen t rails configured to support at least one panel there between.

14. ^'The heiiostat of claim 13, wherein the plurality of secondary supports comprises parallel rails, wherein eac rail comprises a flange, wherei the rails are configured to retain a pane! in two dimensions, such that a panel is permitted to slide in one direction along the rails.

15. The heiiostat of claim 1. wherein the support structure comprises removable struts such that the support structure may be collapsed and expanded.

16. The heiiostat of claim 15, wherein the support structure comprises a cable.